1. Field of the Invention
The present invention relates to a thermal head which is used for heat-sensitive recording, a method of manufacturing the same, a heat sensitive recording method, and more particularly to the improvement of a glaze for obtaining good image quality.
2. Description of the Related Art
As shown in FIG. 6, a thermal head 1 includes glaze 5 which are formed in the direction of a rotational central axis O of a platen 3. A recording material 7 is inserted between the platen 3 and the glaze 5, and the glaze 5 which corresponds to an image to be recorded on the recording material 7 is selectively heated. The image is thermally transferred onto an image receiving surface of the recording material 7 via a toner ribbon 6.
As shown in FIG. 7, in the glaze 5, a convex glaze layer 11 is formed on a ceramic base plate 9. A resistance heat generator 13, an electrode layer 15, a protective layer 17 are laminated onto the glaze layer 11. The electrode layer 15 is divided on the outer surface of the glaze layer 11 so as to form a pair of electrodes. The glaze 5 is constructed in such a way that, as the resistance heat generator 13 between the electrode layers 15 is heated, the glaze 5 performs records onto the recording material 7.
However, in the glaze 5 of the aforementioned conventional thermal head 1, because the electrode layer 15 is divided on the outer surface of the glaze layer 11 so as to secure the heat generating portion of the resistance heat generator 13, the outer surface of the protective layer 17 which is laminated last forms a depressed concave portion 19 due to the non-formation of the electrode layers 15. Namely, the heater portion 18 is formed inside the depressed concave portion 19, especially when the length of the heater portion in the image forming direction of the recording material is less than or equal to 100 .mu.m. The contact between the outer surface of the heater portion 18 and the recording material 7 deteriorates, and there is a problem in that the image quality is adversely effected.
In order to solve this type of problem, as shown in FIG. 8, it was considered that the protruding portions 17a and 17a of the protective layer 17 could be removed by lapping, so that the outer surface of the heater portion 18 would form a flat surface, and the contact between the outer surface of the heater portion 18 and the recording material 7 would be improved. However, since the outer surface of the heater portion 18 formed a flat surface in this configuration, a new problem arose in that a detailed transfer of heat onto the recording material 7 could not be carried out, leading to the microscopic dot density distribution of a highlight portion not being uniform, and the sense of graininess from a macroscopic view increasing.
The present invention was developed in light of the above circumstances, and the object thereof is to provide a thermal head, a method of manufacturing the same, and a heat-sensitive recording method for improving the contact with a recording material and for decreasing the sense of graininess, thereby improving image quality.